Overexpression of the epidermal growth factor receptor (EGFr) is frequently observed in human cancers, notably in breast, head and neck, and non-small cell lung cancer. In the case of breast cancer, EGFr overexpression correlates with poor prognosis. Overexpression usually accompanies autocrine or paracrine TGF-alpha expression, a ligand for the EGFr, which stimulates mitogenesis and contributes to neoplastic transformation. In many instances, overexpression occurs in the absence of gene amplification and is thought to occur through increased transcription of the EGFr gene. The overall aim of this grant application is to identify compounds which selectively block overexpression of the EGFr gene. In Phase I we have identified a cell-type specific transcription terminator which can act as a negative regulatory element in 6 of 7 of the human breast cancer cell lines tested but not in a fibroblast cell line. This element acts as a transcription terminator leading to aborted RNA synthesis. In Phase II we propose to define the precise mechanism through which this negative regulation occurs, and identify the transacting factors involved. We further aim to prepare stably transfected cell lines to be used in drug screens designed to identify lead compounds. Using a novel robotic drug screen capable of screening 3,000 compounds per week against multiple target gene, we propose screening a library of chemical compounds and fungal broths to identify novel compounds for the treatment of human tumors which overexpress EGFr.